1. Field of the Invention
This invention relates generally to metal plate gaskets for use in heavy duty diesel engine applications, and more particularly to the sealing of the combustion chambers of such engines.
2. Related Art
Metal plate gaskets of conventional construction for use in sealing a cylinder head to a block of a heavy duty diesel engine include a solid metal plate formed with a plurality of openings corresponding to various fluid passages communicating between the head and block. At least one of the openings is a combustion opening which surrounds a piston cylinder of the block. A fire ring of copper or the like is set in the plate opening and is crushed to the thickness of the plate as the head is bolted to the block. The fire ring serves to seal the combustion opening against leakage. The plate serves to limit the plastic deformation of the fire ring. One drawback to such fire rings is that they do not recover their shape of the load is removed or decreased. During operation of the engine, the load applied between the head and block varies depending upon the stroke cycle and operating temperature, presenting an opportunity for the head or block to draw away from the fire ring and thus decreasing the sealing effectiveness of such rings.
Other metal plate gasket constructions utilize a conventional, plastically deformable fire ring wrapped in a metal armoring of steel. The steel armor thus relies on the strength and plastic deformation properties of the fire crush ring core to achieve sealing, and thus shares the same deficiencies as the fire ring described previously.
A metal gasket assembly according to the invention comprises a metal gasket plate formed with an opening and having opposing surfaces adjacent the opening to define a predetermined fixed thickness of a plate. An annular grommet is formed separately from the gasket plate from a heat treatable metal so as to be elastically deformable after heat treatment. The grommet has a generally U-shaped body in cross section defining a pair of legs. The legs have outer sealing surfaces spaced a predetermined distance apart to define an initial undeformed thickness that is greater than the thickness of the gasket plate. The opening formed in the gasket plate receives the annular grommet. In use, a compressive force is applied in a generally perpendicular direction to the opposing surfaces of the gasket plate to elastically deform the legs of the body to a reduced thickness corresponding substantially to the thickness of the gasket plate. When the compressive force is released, the legs of the annular grommet return substantially to their original undeformed thickness.
One advantage of the present invention is that the elastically deformable gasket is able to flex with changing load conditions so as to maintain a high integrity seal between a head and block of an engine. As the compressed air/fuel mix burns, its pressure has the tendency to lift the head away from the block, thus lessening the load on the grommet. The grommet responds to such changing conditions by expanding axially under the decreasing load toward recovery of its elastic deformation. As the cycle continues, the grommet is again reloaded and compressed elastically to maintain uniform sealing.
Another advantage of the present invention is that the grommets are made out of less costly material than conventional copper fire rings and may be simply constructed from sheet stock material by suitable stamping and punching operations.
Still another advantage of the present invention is that the elastically deformable grommets may be re-used since they recover their shape on unloading and return to an elastically compressed state upon re-loading.